This API helps developers to detect the current posture of a foldable device. The device posture is the physical position in which a device holds which may be derived from sensors in addition to the angle. From enhancing the usability of a website by avoiding the area of a fold, to enabling innovative use cases for the web, knowing the posture of a device can help developers tailor their content to different devices. Content can be consumed and browsed even when the device is not flat, in which case the developer might want to provide a different layout for it depending on the posture state in which the device is being used.
New types of devices are appearing that have some sort of capabilities that allow them to change their posture. The most common types of devices are the ones that can fold (their screen or around their screen), allowing them to physically alter their form factor.
Samples: https://github.com/foldable-devices